1. Field of the Invention
This invention relates to an electro-surgical instrument of the type having a probe stem which stem has an electrode at its distal end connectable to an HF current source.
2. Description of the Prior Art
Instruments of the type referred to above are well known in the medical field. They are used for so-called electro-coagulation, a technique in which, due to a high field density, the action of an HF current causes overheating in tissue cells which come into contact with the electrode. This overheating causes colloidal matter to precipitate out of the colloidal solution containing it.
An individual electro-surgical instrument, or rather the electrode which comes directly into contact with the biological tissue, has a three-dimensional shape selected to suit its intended purpose. Thus U.S. Pat. No. 3,532,095 and DE-GM 8,423,501 for example disclose electro-surgical instruments which have a spherical electrode at the distal end of the stem, which electrode is arranged in such a way as to be easily exchangeable.
DE-AS 2,324,658 discloses an HF probe for coagulating biological body tissue which, to avoid having a ground electrode of large area, is in the form of a bipolar electrode, having a first, annular electrode and, spaced therefrom, a second electrode of hemispherical shape which forms the distal end of the HF probe.
Another prior art device can be found in DE-0S 2,941,060, which discloses a resection device in which the electrode, through which an HF current flows, is in the form of a loop. The loop can be placed around pieces of tissue which project from bodily surface, such as polyps or the like, so that the piece of tissue can be resected while the area of the cut is coagulated at the same time. The resection loop is longitudinally displaceable within a tubular stem, whereby the width of the resection loop can be varied.
Resection loops are also known from DE-PS 2525982. This document shows how a resection loop can be used for prostate resection and allows tissue to be cut away in strips, that is to say it allows tissue resection whilst coagulating the cut face at the same time.
The structural configuration of the electrodes in probe and loop form which are used for tissue coagulation and resection is matched chiefly to their particular intended purpose, thus making them usable only to a small degree, if at all, for any other purpose.
If, in an endoscopic operation in the rectum for example, there is a need not only for coagulation but also for resection, then in accordance with the state of the art it is necessary to have at least an instrument with interchangeable HF electrodes, or else two separate instruments with specially shaped HF electrodes.
Hence, the disadvantages of known designs lie on the one hand in the fact that HF electrodes which can be secured to the instrument but are exchangeable may be lost in the rectum, and on the other hand; that there is inevitably an additional stress on the patient due to the fact that, both with instruments designed as above and when using a number of specially shaped instruments the time taken by the endoscopic operation is longer because of the time needed to change the instruments.
An object of the invention is therefore to avoid the disadvantages from which these known designs suffer.